Silicone lubricants

ABSTRACT

Lubricant compositions having increased lubricity are obtained by forming a mixture of a major amount of a silicone lubricant and a minor amount of a sulfur containing compound dissolved in the silicone and including at least two sulfur atoms per molecule. According to a preferred form of the invention, from 1 to 10 parts by weight of di-tertiary-nonyl polysulfide are admixed with from 99-90 parts by weight of a silicone oil to provide a new composition which functions properly as a lubricant under loads as high as 240 kilograms when employing the Shell 4Ball EP machine. Without the polysulfide additive, the silicone oil is not useful as a lubricant under loads exceeding about 40 kilograms when employing the Shell 4-Ball EP machine.

United States Patent [72} Inventors Martin J. Devine 2560 Prescott Road,flavertown, Pa. 19083; Edward R. Lamson, Greentree Road, ILD. 4, Sewell,NJ. 08080 [21 1 Appl. No. 783,537 [22] Filed Dec. 13,1968 1451 PatentedSept. 28, 1971 [54] SILICONE LUBRICANTS 6 Claims, 6 Drawing Figs.

[52] U.S. CI 252/463, 252/49.6, 252/327 [5 I 1, Int. Cl Cl0m l/52,C10mI/50,C10mll38 [50] Field of Search 252/463, 45, 47, 47.5; 260/302 SD[56] References Cited UNITED STATES PATENTS 2,206,245 7/1940 Adams eta1. 252/47 X 2,599,917 6/1952 Hommel 252/463 2,719,125 9/1955 Roberts252/467 2,836,564 5/1958 Roberts et a1 260/302 X Devine et a1.Molybdenum Disull'lde Diester Lubricating Greases," NLGI Spokesman, 320-326,.1an. 1964 Primary Examiner- Daniel E. Wyman Assistant Examiner-W.Cannon Attorneys-E. .1. Brower and A. W. Collins ABSTRACT: Lubricantcompositions having increased lubricity are obtained by forming amixture of a major amount of a silicone lubricant and a minor amount ofa sulfur containing compound dissolved in the silicone and including atleast two sulfur atoms per molecule. According to a preferred form ofthe invention, from 1 to 10 parts by weight of ditertiarynonylpolysulfide are admixed with from 99-90 parts by weight of a siliconeoil to provide a new composition which functions properly as a lubricantunder loads as high as 240 kilograms when employing the Shell 4-Ball EPmachine. Without the polysulfide additive, the silicone oil is notuseful as a lubricant under loads exceeding about 40 kilograms whenemploying the Shell 4-Ball EP machine.

PATENTED SEP28 I97! WEAR SCAR DIAMETER (mm.) WEAR SCAR DIAMETER (mm)SHEET 2 [IF 3 Fig 3 3Q A L Q? L40. 7. TL 01...

o 40 so 120 I60 200 240 280 LOAD (kg.)

WEAR SCAR vs /0 DTNP ADDED TO Dc 550 FLUlll) 1HOUR AT |67F 40kg- LoADSTEEL ON STEEL usms SHELL 4 BALL WEAR TESTER Fig. 4

1.0 T I I PERCENT DTNP PATENTEUSEPZBIQYI SHEET smcows- 0 q LUOROSILICONEWEAR SCAR DIAMETER (mm) LOAD (kg.)

WEAR (mm) LOAD (kg.)

SILICONE LUBRICANTS BACKGROUND OF THE INVENTION Silicone oils andlubricants compounded from them are well-known, commercially availablematerials which have presented numerous advantages over other types oflubricant compositions. Generally speaking, for equivalent viscosities,silicone lubricants have (1) lower evaporation rates, (2) smallerchanges in viscosity with unit change in temperature, (3) lower freezingor solidification points, and (4) better oxidation and thermaldegradation resistance than other types of lubricants. However, a majordisadvantage of such silicone lubricants is their poor load-carryingcapacities. In this respect, the silicone lubricants are considerablyless useful than most other classes of lubricants, including thecommonly used petroleum and diester lubricants. In fact, the ability ofthe silicone lubricants to lubricate steel vs. steel combinations insliding motion under boundary conditions is practically nil. Thewell-known antiwear and EP additives which are readily soluble in thepetroleum and diester lubricants cannot be employed with siliconesbecause of their poor solubility therein.

SUMMARY OF THE INVENTION This invention relates to silicone lubricantcompositions and has for an object greatly increasing thewear-prevention properties of a silicone lubricant, especially underconditions of sliding motion, by adding thereto a sulfur containingcompound soluble in the silicone and including at least two sulfur atomsper molecule.

Unexpectedly, we have discovered that the addition, to a siliconelubricant. of a minor amount of a sulfur-containing compound dissolvedin that lubricant and including two or more sulfur atoms per moleculesignificantly enhances the lubricity properties of the silicones,thereby, greatly extending the applications to which such siliconelubricants can be directed.

in general, any of the well-known silicone fluids and greases may beused to provide the lubricant compositions of the invention. Suchsilicone lubricants generally are liquids, or solids liquifiable onwarming. As used herein, the term silicone lubricant" includes thewell-known organopolysiloxanes and organosilanes, silicate esters,silarylene-type compounds, such as silphenylene, as well as alkyl andaryl disilazane such as hexamethyl disilazane, for example.

Among the organopolysiloxanes which may be used to provide the lubricantcompositions of the invention are those having the formula I nr nmmwhere R represents a member selected from the class consist ing of alkylradicals (e.g., methyl, ethyl, propyl, isopropyl, butyl, octyl, etc.radicals); cycloalkyl radicals (e.g., cyclohexyl, cycloheptyl, etc.,radicals); aryl radicals (e.g., phenyl, diphenyl, naphthyl, etc.,radicals); alkaryl radicals (e.g., tolyl, xylyl, ethylphenyl, etc.,radicals); aralkyl radicals (e.g., benzyl, phenylethyl, etc., radicals);haloaryl radicals (e.g., monochlorophenyl, dibromophenyl,tetrachlorophenyl, monofluorophenyl, etc., radicals); cyanoalkylradicals (e.g., cyanomethyl, Bcyanomethyl, rcyanopropyl, etc.,radicals). Preferably at least 50 mole percent of the R groups are loweralkyl groups having from one to two carbon atoms, preferably the methylradical, and m has a value from 1.98 to 3. Examples of suchorganopolysiloxanes are given in Patnode U.S. Pat. Nos. 2,469,888 and2,469,890, and in Pfeifer U.S. Pat. No. 2,704,748, wherein are disclosedlinear as well as branchchuined organopolysiloxanes coming within theabove formula as well as cyclic organopolysiloxanes, e.g.,hexamethylcyclotetrusiloxune. octamethylcyclotetrasiloxane,tetraphenyltetramethylcyclotetrasiloxane, octaethylcyclotetrasiloxane,etc.

The silicate ester lubricants which can be used to provide thecompositions of the invention will generally correspond to the formulawhere R,, R R and K, may be the same or different and are selected fromthe same class of radicals as designated for R in formula I above.

The silarylene-type materials useful to provide the lubricantcompositions of the invention will generally comprise polymericmaterials characterized by recurring structural units of the formulawhere R R R and R are the same or different and are selected from thesame class of radicals as R above, and A is an arylene radical (e.g.,phenylene, diphenylene, naphthylene, etc. radicals); alkarylene radicals(e.g., tolylene, xylylene, ethylphenylene, etc. radicals); haloaryleneradicals e.g., monocholorophenylene, dibromophenylene,tetrachlorophenylene, monofluorophenylene, etc., radicals).

Other examples of silicone fluids which can be used in the practice ofthe invention may be found in Synthetic Lubricants, R. C. Gunderson andA. W. Hart, Reinhold Publishing Corp. I962.

In general, any sulfur-containing compound, soluble in the siliconelubricant with which it is to be admixed, and including at least twoatoms of sulfur per molecule, may be employed to provide the improvedsilicone lubricants of the invention. Among the sulfur containingcompounds which may be used are those having the formula where R,, and Rare hydrocarbon radicals which can be the same or different, and whichare selected from the same class of radicals as R above, and x is anumber from 1 to about 20.

One particular group of sulfur compounds which can advantageously beused are those corresponding to the general formula where R and R arethe same or different hydrocarbon radicals selected from the same classof radicals as R above, a and b are whole numbers from 0 to about 8, thesum of a and b being at least I, and preferably 2 to about 16. Specificexamples of polysulfides falling within the scope of the above formula,as well as methods of their preparation, can be found in US. Pat. No.2,719,125-Roberts.

Specific examples of sulfur compounds which can be employed in thepractice of the present invention are, for instance, tetraethyl thiuramdisulfide, antimony diamyl dithiocarbamate, antimony diamylphosphordithioate, di-tertiary butyl polysulfide, di-tertiary amylpolysulfide, di-tertiary octyl polysulfide, di-tertiary-nonylpolysulfide, di-tertiary dodecyl polysulfide and the disulfidederivative of 2,5-di-mercapto-l ,3,4-thiadiazole, and polysulfidepolymers such, for example, as those corresponding to the formula Otherexamples of suitable polysulfides which are soluble in the siliconelubricant with which they are to be admixed and which include at leasttwo sulfur atoms per molecule will readily occur to those skilled in theart.

The amount of the sulfur-containing compound used in the practice of thepresent invention can be varied within wide limits. Satisfactory resultscan be obtained in improving the wear-resistant properties of thesilicone lubricant by adding to the silicone from as low as aboutone-tenth of 1 percent to as high as 25 percent or more, based upon thetotal weight of the silicone lubricant plus sulfur compound employed.Preferably, the amount of the sulfur compound advantageously employed isthe minimum required to impart the desired load-carrying characteristicsto the silicone lubricant that is used. It is essential in thisconnection that the sulfur compound used be dissolved in the silicone inthe amount employed so as to form a homogeneous solution therewith.Preferably, therefore sulfur compounds which are soluble in the siliconeshould be employed. In instances where the sulfur-containing compound isnot soluble in the silicone, adequate solubility may be obtained byemploying a small amount of a common solvent for the silicone and thesulfur compound so as to facilitate the production of a homogeneoussolution of the sulfur compound in the silicone. Such common solventswill readily occur to those skilled in the art.

DESCRIPTION OF DRAWINGS AND PREFERRED EMBODIMENTS Referring now to thedrawings, FIGS. I-6 respectively present the results of test of aplurality of silicone lubricants with and without soluble sulfuradditives which include two or more sulfur atoms per molecule.

A Shell 4-Ball Extreme Pressure Tester was used for the comparisonpresented in the graphs of FIGS. 1-6, inclusive. The pressure testerused to compile the data shown in FIGS. [-3, 5 and 6 is an acceptedtesting device comprising three balls which are maintained stationaryand located 120 apart. A fourth ball is supported by the threestationary balls, all of them being of steel. In the test, the steelballs were of the composition of specification AISI-C52 100.

Referring now to FIG. 1, the ball supported by the other three wasrotated with an initial load of about 20 kilograms. The four-ball testerincludes a cup within which the balls are located, and which is filledwith the lubricant whose lubricity is to be tested. Curve 10 was drawnfrom data acquired when the cup was filled with apoly(methyl-phenyl)siloxane containing no additive. After rotation ofthe supported steel ball at 1,800 revolutions per minute for 10 seconds,the test was terminated and the wear scar diameter measured. The fourballs, or test specimens, are one-half inch in diameter and thereference to wear scar diameter is the width of the brightened and worncircular area produced on the stationary ball. With initial loading(kg), this wear scar diameter had a width of 0.75 millimeters. The fourballs were then replaced and the load was increased to kilograms. Thewear scar diameter had increased to about 1.42 millimeters. At 75kilograms load, the wear scar diameter had further increased to 2.15.

We have found that the addition of an organic compound having at leasttwo or more sulfur atoms per molecule dissolved in the silicone liquidgreatly decreases the wear. The addition of but one-tenth of a percentof the sulfur-containing additive results in a discernible improvement.If only 1 percent be added, then a load of 40 kilograms up to 1 l0kilograms was found to result in a wear scar diameter not exceedingabout 1.375 millimeters. As a matter of fact, with a load of 75kilograms, the curve 11 indicates a decrease in wear scar diameter to1.25. As the load is further increased to 220 kilograms, it will be seenthat the scar diameter increased more or less linearly until the valueof about 200 kilograms was reached, and then increased at a much morerapid rate, seizure having taken place at the load of 220 kilograms.

By adding 5 percent of the sulfuncontaining compound, in this case thedi-tertiary-nonyl polysuliide in 5 percent of the weight, the initialscar diameter at 40 kilograms load had not increased beyond itsmagnitude at 20 kilograms (see curve 12). There was then the unexpecteddecrease in scar diameter to 75 kilograms load with a gradual rise inscar diameter until a loading of 240 kilograms was reached. At thisheavy loading, the scar diameter was only 1.35 in contrast with the scardiameter for the silicone liquid without additive of 2.27 at kilogramsof load, and as compared with a scar diameter of about 1.9 for the 1percent of additive at a load of 220 kilograms.

Curve 13 shows the results obtained by the addition of 10 percent byweight of di-tertiary-nonyl polysulfide to the silicone employed. Thescar diameter was depressed throughout the loading with the final scardiameter at 240 kilograms about the same as that for the 5 percentaddition.

The results as presented by the curves of FIG. 1 demonstrate thatsilicone lubricants have been provided with greatly increasedwear-resistant characteristics which now make them suitable for a widevariety of applications for which the silicones alone were whollyunsuited.

While we prefer to describe lubrication where the oil film is maintainedbetween the bearing surfaces as hydrodynamic, we recognize that othersrefer to such characteristics as complete or viscous lubrication,meaning that the friction developed arises due solely to the internalfluid friction in the film. This simply means that in hydrodynamiclubrication, the surfaces are separated. In respect of boundarylubrication, the lubricating film becomes extremely thin and we considerthat this encompasses surface-to-surface contact.

Referring now to FIG. 2, curve 14 illustrates the relationship betweenload and wear scar diameter for a chlorinated silicone available on themarket as Dow Corning 560. Here it will be seen that between the loadingof 20 to 80 kilograms, the scar diameter rapidly increased to 1.65, atwhich time seizure occurred. The addition of 10 percent ofdi-tertiarynonyl polysulfide completely changed the wearcharacteristics. The initial scar diameter was less, and at a loading of240 kilograms, it has increased to 1.25, the scar diameter without theadditive having been attained as shown by curve 14, at about 55kilograms load.

Table I below sets forth the wear scar diameters (in millimeters)obtained from testing, at various load levels,poly(methyl-phenyl)siloxane alone, and in admixture with 5 percent byweight of various alkyl polysulfides corresponding to the formula inwhich R was an alkyl from four to 12 carbon atoms.

The results set forth in the foregoing table also make clear theunexpectedly decreased wear to bearings operating under heavy load whenlubricated with the compositions of the present invention.

FIG. 3 shows a comparison of wear scar diameters attained at variousloads in the test apparatus using silphenylene lubricant alone, andsilphenylene lubricant including 10 percent by weight ofdi-tertiary-nonyl polysulfide. FIG. 3 thus demonstrates that thesilphenylene fluid afiords little wear resistance since the wear scardiameter rapidly increases from a value of just below 0.7 millimeters at20 kilograms load to over 2.2 millimeters at 80 kilograms load. On theother hand, the addition of 10 weight percent of di-tertiary-nonylpolysulfide extended the permissible load to 240 kilograms with a scardiameter of only 1.2 millimeters.

FIG. 4 illustrates the effect on lubricity of increased addition to thesilicone lubricant of a sulfur-containing compound in accordance withthe invention. In this instance, the Shell 4- Ball Wear Test wasconducted. FIG. 1 demonstrates that the addition of only one-half of 1percent of the sulfur additive (di-tertiary-nonyl polysulfide)materially decreases the scar diameter. The chart shown in FIG. 4 alsodemonstrates that the optimum amount of sulfur compound addition is atabout 8 percent, based on the weight of the silicone liquid used.

FIG. 5 shows the results of tests made on a fluorosilicone lubricantalone, compared to the fluorosilicone lubricant containing percent byweight of the di-tertiary-nonyl polysultide. It will be observed thatthe fluorosilicone without the additive is useful as a lubricant up toabout 130 kilograms load, at which point, any additional loading greatlyincreases the scar diameter. In contrast, the composition of theinvention comprising the fluorosilicone including 10 weight percent ofdi-tertiary-nonyl polysulfide extends the usefulness of the lubricant toa loading in excess of 280 kilograms and with a scar diameter of only1.25 millimeters.

FIG. 6 illustrates the unexpected results achieved by adding to thesilicone lubricant 10 weight percent of a polysulfide comprising analkyl derivative of 2,5-di-mercapto-1,3,4- thiadiazole.

The following table 11 sets forth the data obtained from an oscillatormotion test conducted with an organic dye thickenedp0ly(methyl-pheny1)siloxane with, and without, a sulfur compoundadditive (alkyl derivative of 2, S-di-mercapto-b 1, 3, 4Thiadiazole ofthe type disclosed in US Pat. No. 2,719,125).

TABLE I1 Cycles to Failure Siloxane alone 577 Siloxane plus 5; by weightof sulfur additive 2.385

Test Conditions A1514620 steel ring oscillation against a stationaryA1S14l30 steel block. Grease Properties Penetration (worked 60 strokes)297 Dropping point 450 F. Oscillations/Min. 87.5

Load 90 lbs. Temperature 77 F.

The following table 111 sets forth the wear scar diameters (in mm.)obtained at various load levels using a poly(methylphenyl)siliconemodified with 15 percent di-tertiary-nonyl polysulfide and with 25percent of said polysulfide. The Shell 4-Ball EP Tester was used.

Table IV below sets forth the wear scar diameters (in mm.) obtained atvarious load levels using (a) poly(methyl-phem yl)siloxane plus 10percent by weight di-tertiarynonyl polysulfide, (b)poly(methyl-phenyl)siloxane siloxane plus 10 percent by weight of analkyl derivative of 2,5-di-mercapto- 1,3 ,4-thiadiazole; and (c)poly(methyl-phenyl)siloxane plus 5 percent by weight ofdi-tertiary-nonyl polysulfide and 5 percent by weight of an alkylderivative of 2,5-di-mercapto-l ,3,4- thiadiazole. The Shell 4-Ball EPTester was used.

TABLE IV SCAR DIAMETERS (mm.) AT VARIOUS LOADS at 40kg. at kg. at l20kg.at l80kg. at 240kg.

TABLE V WEAR SCAR DIAMETER (mm.) AT VARIOUS LOADS g) at 40 at 60 at atat 200 with (a) 1.4 1.9 3.3 with (b) 1.0 0.38 1.0 1.11 123 with (a) 2.63.1 with(b) 1.31 1.51 1.94 2.38 1.87

The following table VI sets forth the values of wear scar diameters (inmm.) at various loads using, as a lubricant, (a)poly(methyl-phenyl)siloxane; (b) poly(methyl-phenyl)silox ane plus 10percent by weight of di-2-ethyl hexyl sebacate (a well-known and widelyused diestcr fluid); (c) poly(methylphenyl)siloxane with 9.5 weightpercent di-Z-ethyl sebacate and 5 percent by weight of di-tertiary-nonylpolysulfide; and (d) 85.05 weight percent poly(methyl-phenyl)siloxane,9.45 weight percent di-2-ethyl hexyl sebacate, 5 percentdi-tertiarynonyl polysulfide and 0.5 percent phenyl alphanaphthylamine(a well-known antioxidant). The Shell 4-Ball EP Tester was used.

TABLE V1 WEAR SCAR DIAMETERS (mm.) AT VARIOUS LOADS g) at 80kg. atl20kg. at 240kg.

(a) 2.2 3.3 weld (b) 2.7 weld Weld It should be understood that whilethe present invention has been described in considerable detail withrespect to certain specific embodiments thereof, it is not to beconsidered limited to those embodiments, but may be used in other wayswithout departure from the spirit of the invention or the scope of theappended claims.

What is claimed is:

l. A lubricant composition consisting essentially of a major proportionof an organic silicon-containing lubricant selected from the classconsisting of organopolysiloxanes, organosilanes, silicate esters,silarylenes, and alkyl and aryl disilazanes, having dissolved therein aminor proportion, sufficient to improve the load-carrying properties ofsaid organic silicon-containing lubricant, of a sulfur-containingcompound selected from the group consisting of:

a. a di-tertiary alkyl polysulfide wherein the alkyl group includes fromfour to 12 atoms;

b. a compound having the general formula l-lS-(C H,- OCH OC H.,S ),-C HOCH --OC H -SH wherein x is 6 or 23; and

c. a hydrocarbon polysulfide derivative of2,5dimercaptol,3,4,-thiadiazo1e having the general formula wherein R andR are the same or different hydrocarbon radicals selected from the classconsisting of alkyl, cycloalkyl, aryl, alkaryl, aralkyl, haloaryl, andcyanoalkyl radicals; and a and b are whole numbers from O to about 8,the sum of a and b are whole numbers from to about 8, the sum of a and bbeing at least 1.

2. The lubricant composition of claim 1 in which the sulfur containingcompound ranges from about 0.1 percent to about 25 percent by weight ofthe total weight of said silicone and said sulfur-containing compound.

3. The lubricant composition of claim 1 in which the sulfurcontainingcompound is a hydrocarbon polysulfide derivative of2,5-dimercapto-l,3,4,-thiadiazole having the general formula wherein Rand R are the same or different hydrocarbon radicals selected from theclass consisting of alkyl, cycloalkyl, aryl, alkaryl, aralkyl, haloaryl,and cyanoalkyl radicals; and a and b are whole numbers from 0 to about8, the sum of a and b being at least 1.

4. The lubricant composition of claim I wherein the sulfurcontainingcompound comprises a compound having the general formula H--S(C H -OCH-O-C H -S C H,0CH OC,H -S-H wherein x is 6 or 23.

5. The lubricant composition of claim 1 wherein the sulfurcontainingcompound comprises a di-tertiary alkyl polysulfide wherein the alkylgroup includes from four to 12 carbon atoms.

6. The lubricant composition of claim 5 wherein the sulfurcontainingcompound is di-tertiary-nonyl polysulfide.

U.S. PATENT OFFICE UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No. 3,609,079 t September 28, 1971 Martin J. Devine and Edward R.Lamson It is certified that errors appear in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

Column 7, lines 29 and 30, delete the phrase "the sum of g and l o arewhole numbers from 0 to about 8,

Signed and sealed this 21st day of November 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR.

Attesting Officer ROBERT GOTTSCHALK Commissioner of Patents

2. The lubricant composition of claim 1 in which the sulfur containingcompound ranges from about 0.1 percent to about 25 percent by weight ofthe total weight of said silicone and said sulfur-containing compound.3. The lubricant composition of claim 1 in which the sulfur-containingcompound is a hydrocarbon polysulfide derivative of 2,5-dimercapto-1,3,4,-thiadiazole having the general formula wherein R11and R12 are the same or different hydrocarbon radicals selected from theclass consisting of alkyl, cycloalkyl, aryl, alkaryl, aralkyl, haloaryl,and cyanoalkyl radicals; and a and b are whole numbers from 0 to about8, the sum of a and b being at least
 1. 4. The lubricant composition ofclaim 1 wherein the sulfur-containing compound comprises a compoundhaving the general formulaH-S-(C2H4-O-CH2-O-C2H4-S2)x-C2H4-0-CH2-O-C2H4-S-H wherein x is 6 or 23.5. The lubricant composition of claim 1 wherein the sulfur-containingcompound comprises a di-tertiary alkyl polysulfide wherein the alkylgroup includes from four to 12 carbon atoms.
 6. The lubricantcomposition of claim 5 wherein the sulfur-containing compound isdi-tertiary-nonyl polysulfide.